Process for the production of sulfited polyesters and their use as retanning agents - Patent Application 20070122997

Abstract

The present invention provides a process for the production of sulfited polyesters by esterification of an unsaturated carboxylic acid or anhydride thereof and optionally a saturated carboxylic acid or anhydride thereof with a polyol under mild conditions generally below 180° C., preferably below 160° C., and subsequent sulfitation under mild conditions generally below 180° C., preferably below 160° C. The sulfited polyesters can be used as retanning agents in the leather process.

Description

[Technical Field]

[0001] The present invention relates to a novel process for the production of sulfited polyesters and the use of the resulting sulfited polyesters as retanning agents in the leather manufacturing process.

[0002] Leather is a durable, flexible material produced through the tanning process of raw animal hides and skins. The leather manufacturing process is divided into three basic sub-processes: preparation, tanning, and crusting.

[0003] The present invention relates to the sub-processes of the tanning process, particularly the retanning portion.

[0004] The preparation stage prepares the hide or skin for the tanning process. After trimming, the animal hide is soaked to remove salt and other solids, while also restoring moisture as the hide initially dries. The flesh side of the wet hide is then scraped to remove any remaining traces of meat or fat, and the hide is optionally dehaired. After optional baiting and pickling steps, the hide is subjected to the tanning process. Other potential steps that may be part of the preparation stage include curing, liming, splitting, reliming, deliming, degreasing, fridging, bleaching, and de-picking.

[0005] Tanning is the process by which the proteins of raw hides or skins are transformed, through the cross-linking of collagen fibers, into a stable material that will not decay and has satisfactory properties, such as a high shrinkage temperature T S The process of preserving hides by providing tanned leather that has good suppleness and suitability for subsequent treatments such as neutralization, retanning, fatliquoring, dyeing, finishing, etc.

[0006] Tanning is primarily carried out by treating hides with organic reactive tanning agents, such as chromium sulfate (giving so-called wet blue leather) or aldehydes, especially glutaraldehyde (resulting in wet white leather). Rarely, tanning is carried out using vegetable tanning agents, as traditionally done, or synthetic tanning agents (syntans), or other conventional techniques. The products prepared in this subprocess are intermediate because they are not sufficient to obtain the desired properties specified by the customer. Therefore, tanned hides are further treated with various products. This process is called retanning. Retanning affects other factors, such as leather feel, dyeability, leather solidity, grain fineness, grain stability, and lightfastness, to suit the properties required for the final leather article (automobile or aircraft seat, footwear, clothing or bags, and leather goods). The retanning process includes dyeing to impart color, and fatliquoring to add softness, solidity, and feel. Once the retanning process is complete, the leather is known as "crust."

[0007] Vegetable tanning agents were the first tanning agents. Nowadays, they are mainly used for retanning, as chromium sulfate or glutaraldehyde are widely accepted as tanning agents. Common vegetable tanning agents are mimosa, obtained from the bark of the acacia tree, and tara, obtained from the fruit of the tara bush. They can impart flexibility and limited filling to the collagen structure of leather (Hans Herfeld, "Library of Leather; Volume 3: Tanning Agents, Tanning and Retanning," Frankfurt 1985, page 44). Vegetable tanning agents typically lack fastness properties, such as resistance to light or heat-induced aging.

[0008] The term syntan refers to a range of synthetic tanning agents. The first syntans were prepared by the condensation of phenolsulfonic acid with formaldehyde (E. Stiasny, 1911, Austrian Patent No. 58405). These syntans were initially used as dispersants and adjuvants for vegetable tannins, but after further development of their chemistry, they could be adapted to replace some or all of the vegetable tannins. US 1,841,840 describes how such further development can be achieved by incorporating urea into the polycondensation of phenolsulfonic acid with formaldehyde, as shown in Scheme 1, making it possible to obtain leathers that meet increased technical requirements, such as fastness properties with respect to light- or heat-induced aging.

[0009] [ka] With chromium sulfate or glutaraldehyde becoming widely accepted as tanning agents, syntan is currently used primarily in retanning processes to help structure and fill the cross-linked collagen fibers. Unfortunately, syntan can contain residual amounts of undesirable by-products such as free formaldehyde or bisphenol S or F, which means that it must be handled and used with care due to safety reasons.

[0010] In many applications, both syntan and vegetable tannins are used because the performance of vegetable tannins alone is considered insufficient. Syntans generally have better fastness properties and also have dispersing properties, which help to support the uniform distribution of vegetable tannins and other leather chemicals such as fillers, dyes, and fatty liquors (DE1142173).

[0011] In view of the fact that syntan is still oil-based and made from toxic phenol and formaldehyde, a search is underway for retanning agents made from less toxic starting materials, preferably renewable starting materials, that can replace syntan. There is a continuing need for chemical products made from bio-based materials instead of petroleum-based materials, and these bio-based materials are referred to as renewable materials. Currently, corporate responsibility and the use of sustainable or renewable raw material sources are major drivers for companies, especially the chemical industry. Of particular interest is the use of bio-based raw materials that do not compete with the use of those bio-based raw materials as food sources, and therefore the use of bio-based waste streams is particularly beneficial.

[0012] EP 3597778 B1 describes condensation products of dicarboxylic acids having 2 to 6 carbon atoms with diethanolamine, which give mixed polyesters and polyamides as tanning, retanning or pretanning agents.

[0013] CN10275752 discloses water-soluble furandicarboxylic acid-containing aromatic polyesters having high sulfonate-containing compound contents of more than 12 mol % in the examples.

[0014] US 4,525,524 describes polyesters having sulfonate groups, which are incorporated by reaction with sulfophthalates or their alkyl esters, which results in aromatic groups being present in the resulting polyesters having sulfonate groups.

[0015] US 3,915,950 describes the sulfurization of unsaturated polyester products with sulfur in the presence of zinc oxide using heat to provide sulfurized products for use as additives in lubricating oils.

[0016] GB 1298204 describes the synthesis of flexible unsaturated polyesters from polyether diols and ethylenically unsaturated dicarboxylic acids or their anhydrides.

[0017] GB 1214087 describes the synthesis of polyesters with sulfonate groups, which are incorporated by reacting a phenolsulfonate salt with a dicarboxylic acid and a diol.

[0018] JPS 58122917 describes the synthesis of sulfite polyesters, but the manufacturing process uses harsh conditions for both the esterification (over 190°C) and sulfitation (170-250°C and acidic conditions) steps, and zinc acetate is used in the esterification step. The resulting polyesters with sulfonate groups are described as being usable as textile adhesives, paper processing agents, textile processing agents, adhesives, paints, water-soluble films, binders, or anionic functional resins. The presence of zinc in the final product is no longer desirable today.

[0019] US 3,018,272 discloses the use of polyesters having -SO3M groups (where M is a metal) as basic dye-sensitizing units that allow the fibers to be easily dyed using basic dyes.

[0020] US 6,576,717 describes a water-dispersible acrylic-modified polyester resin containing sulfonate groups prepared by addition copolymerization of an ethylenically unsaturated vinyl monomer with a polyester. The polyester is prepared from a polycondensation reaction of a dicarboxylic acid, a glycol, an ethylenically unsaturated monomer, and a small amount of a sulfomonomer.

[0021] AAIbrahim published the use of hyperbranched poly(amidoamine) as a pretanning agent for leather starting with methyl acrylate and diamine (International Journal of Polymer Science 2013, 5154). The pretanning agent increases the amount of chromium absorbed during the tanning process, which is beneficial.

[0022] The present invention provides a process for obtaining sulfited polyesters under mild conditions, which are formaldehyde- and bisphenol-free and can be used as retanning agents in leather processes, providing good retanning behavior.

[0023] It has been found that polyesters can be converted under mild conditions into water-soluble sulfited compounds suitable for aqueous applications. Surprisingly, it has been found that the resulting sulfited polyesters can be used as retanning agents and thus can replace syntan in the retanning process of leather. Prior art sulfited polyesters obtained via different processes are also suitable for use as retanning agents and can therefore replace syntan in the retanning process of leather.

[0024] It is an object of the present invention to provide a process for the esterification of unsaturated carboxylic acids, optionally saturated carboxylic acids, with polyols under mild conditions, and subsequent sulfitation.A further object of the present invention is to provide sulfited polyesters that can be used as retanning agents in leather processes, which are formaldehyde- and bisphenol-free, provide good retanning behavior, and are preferably made from partially renewable raw materials.

[0025] In a first aspect, the present invention relates to a process for the preparation of sulfited polyesters by esterification under mild conditions of an unsaturated carboxylic acid or anhydride thereof (and optionally a saturated carboxylic acid or anhydride thereof) with a polyol, and subsequent sulfitation under mild conditions.

[0026] In a second aspect, the present invention relates to the use of a product obtained by esterification under mild conditions of an unsaturated carboxylic acid or anhydride thereof (and optionally a saturated carboxylic acid or anhydride thereof) with a polyol, and subsequent sulfitation under mild conditions, as a retanning agent in the leather making process.

[0027] In a third aspect, the present invention relates to the general use of sulfited polyesters as retanning agents in leather making processes.

[0028] The water-soluble sulfited compounds of the present invention are obtained by condensing a polyol with a carboxylic acid, some or all of which contain one or more double bonds, and then reacting with a sulfite to form a water-soluble sulfited polyester, which is a polyester having sulfonate groups. The molar ratio of saturated to unsaturated acids ranges from 0:1 to 5:1. Saturated acids can be absent (meaning a 0:1 ratio), but their presence is beneficial to their performance as retanning agents. Unsaturated acids are necessary because they can be sulfited, and sulfiting results in water solubility. If the ratio is greater than 5:1, meaning there are more than five times as many saturated acids than unsaturated (those that are subsequently sulfited), water solubility decreases to a critical value, which is undesirable.

[0029] Both saturated and unsaturated carboxylic acids are preferably dicarboxylic acids, although in addition to dicarboxylic acids, small amounts of monocarboxylic acids, tricarboxylic acids, or polycarboxylic acids may also be present. The amount of monocarboxylic acid should not be too high because the monocarboxylic acid functions as a chain terminator. The amount of tricarboxylic or polycarboxylic acid should not be too high because the tricarboxylic and polycarboxylic acids cause branching of the polymer chain and thus increase viscosity. In the context of the present invention, the molar ratio of monocarboxylic acid to dicarboxylic acid (for unsaturated and saturated acids) is preferably 0:100 to 25:75, most preferably 0:100 to 10:90. In the context of the present invention, the molar ratio of tricarboxylic or polycarboxylic acid to dicarboxylic acid is preferably 0:100 to 10:90, most preferably 0:100 to 5:95.

[0030] Both the esterification and sulfitation steps were carried out under mild conditions, i.e., at moderate temperatures, e.g., below 180° C., preferably below 160° C. for the esterification reaction, and below 100° C., preferably below 90° C. for the sulfitation reaction. In addition, the sulfitation reaction is carried out at a mild pH value, e.g., a pH value of 6-10, preferably 7-9.

[0031] The sulfite polyesters can be used as retanning agents for tanned hides. A general reaction sequence using itaconic acid as an example of an unsaturated dicarboxylic acid is shown in Scheme 2.

[0032] [ka] The present invention is not limited to itaconic acid, and therefore, any other unsaturated carboxylic acid, or mixtures thereof, may be used. Examples of unsaturated dicarboxylic acids include maleic acid, fumaric acid, glutaconic acid, traumatic acid, citraconic acid, and mesaconic acid. Examples of unsaturated monocarboxylic acids include fatty acids such as myristoleic acid, sapienic acid, α-linolenic acid, stearidonic acid, eicosapentaenoic acid, cervonic acid, linoleic acid, linoledic acid, γ-linolenic acid, dihomo-γ-linolenic acid, arachidonic acid, docosatetraenoic acid, palmitoleic acid, vaccenic acid, paulic acid, oleic acid, eleic acid, gondoic acid, erucic acid, nervonic acid, and mead acid. An example of an unsaturated tricarboxylic acid is aconitic acid. The present invention is also not limited to carboxylic acids as starting materials, as anhydrides such as itaconic anhydride or maleic anhydride may also be used.

[0033] Unsaturated dicarboxylic acids can be condensed in the presence or absence of other dicarboxylic, tricarboxylic, or polycarboxylic acids, as illustrated in Scheme 3.

[0034] [ka] The polyol used in the present invention can be linear or branched, can contain other functional groups, and can be any component containing two or more hydroxyl groups, or a combination of such components, such as a monomeric diol, a monomeric triol, a polymeric diol, or a polymeric triol, or a combination thereof. Examples of monomeric polyols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, bis(hydroxyethyl) terephthalate, neopentyl glycol, trimethylolpropane, cyclohexanedimethanol, furandiethanol, glycerol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,8-octanediol. In addition to monomeric polyols, polymeric polyols such as polyester polyols, polyesteramide polyols, polyether polyols, polythioether polyols, polycarbonate polyols, polyacetal polyols, polyolefin polyols, or polysiloxane polyols, or mixtures thereof, can also be used.

[0035] Preferably, at least one of the unsaturated monocarboxylic and polycarboxylic acids and saturated monocarboxylic or polycarboxylic acids and / or polyols used in the present invention is biobased. Examples of biobased saturated dicarboxylic acids include oxalic acid, succinic acid, adipic acid, glutaric acid, and azelaic acid. Preferred examples of monounsaturated dicarboxylic acids include itaconic acid, a biobased product primarily produced by fermentation using certain filamentous fungi, and citraconic acid and mesaconic acid, both of which can be prepared from biobased citric acid. Examples of biobased unsaturated monocarboxylic acids include various fatty acids such as palmitoleic acid, vaccenic acid, or oleic acid. Examples of biobased saturated monocarboxylic acids include stearic acid, lauric acid, myristic acid, and palmitic acid. Examples of bio-based polyols include 1,2-ethanediol, 1,3-propanediol, glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, galactitol, fucitol, iditol, inositol, volemitol, isomalt, maltitol, and lactitol.

[0036] The potential combination of bio-based unsaturated mono- and polycarboxylic acids, bio-based saturated mono- and polycarboxylic acids, and bio-based polyols offers many possibilities for establishing opportunities to move away from oil-based products such as syntans to obtain polyesters with high or completely bio-based content.

[0037] The resulting sulfited polyester preferably has greater than 50% of its carbon atoms derived from sources that may be biobased.

[0038] The esterification of the carboxylic acid with the polyol proceeds in the presence of an acid that acts as a catalyst, while the water formed is removed by distillation. Examples of acids that can be used as catalysts are mineral acids such as sulfuric or phosphoric acids, or organic acids such as sulfonic acids. These acids remain in the product.

[0039] Esterification of the anhydride with the polyol can be accomplished without a solvent or catalyst by heating the polyol with the anhydride. In another embodiment, a preformed polyester can be reacted with the anhydride, the preformed polyester having been previously synthesized from an ester and a polyol in a ratio such that the preformed ester has hydroxyl end groups.

[0040] The esterification of the carboxylic acid or anhydride with the polyol is achieved under relatively mild conditions, at a reaction temperature of 120°C to 180°C, preferably 140°C to 160°C, for a reaction duration of 1 to 3 hours, with the reaction time being longest at the lowest reaction temperature and shortest at the highest reaction temperature.

[0041] The esterification of the unsaturated carboxylic acid with the polyol may be carried out in the presence of a small amount of a free radical scavenger to ensure that the double bond of the unsaturated dicarboxylic acid remains unreacted. Examples of such free radical scavengers include hydroquinone, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ), and 4-methoxyphenol.

[0042] The sulfitation reaction of the present invention generally uses NaHCO3 and sodium bisulfite (NaHSO3), or sodium sulfite (Na2SO3), or sodium metabisulfite (Na2SO5) to convert carbon-carbon double bonds, olefinic bonds, into sulfonates under mild conditions, followed by the effective attachment of hydrogen and a SO3 Na group to the former C=C double bond, as shown in Scheme 2. In the context of the present invention, the degree of sulfitation is 95% or higher, preferably 98% or higher, and most preferably 99% or higher, which refers to the percentage of conversion of olefinic bonds to sulfonates. The completeness of the sulfitation reaction can be verified by measuring the NMR spectrum of the mixture, and the sulfitation can be deemed complete when signals from olefinic bonds at 5 ppm to 6 ppm can no longer be detected in the spectrum. This sulfitation reaction is achieved under relatively mild conditions, at temperatures between 50°C and 120°C, preferably between 60°C and 100°C, and most preferably between 70°C and 90°C. The reaction is carried out for a certain duration, which depends on the reaction temperature; preferably, the reaction duration is 1 to 5 hours, most preferably 1 to 3 hours, with the reaction time being longest at the lowest reaction temperature and the reaction time being shortest at the highest reaction temperature.

[0043] The inventors have found that sulfited polyesters, such as those obtained from the process of the present invention, can be applied to leather, such as through industry-standard procedures for retanning. Surprisingly, leather treated with sulfited polyesters, preferably made with partially renewable ingredients, was found to impart similar or better properties to leather than syntan or vegetable tannins in terms of flexibility, solidity, and lightfastness, while not creating bisphenol or formaldehyde issues. Analysis for toxic formaldehyde or bisphenols is not actually necessary for these sulfited polyesters, because none of the components contain or can release formaldehyde or form bisphenols. These sulfited polyesters represent a novel, non-toxic, and partially renewable alternative to oil-based phenol-formaldehyde condensates in the leather industry.

[0044] The retanning agent comprising the sulfited polyester can also be combined with other ingredients such as lignin, starch, chitin, kaolin, or protein in the retanning composition.

[0045] The industry-standard procedure for retanning involves treating tanned leather, such as wet blue, with water, sodium formate, and sodium bicarbonate for a period of time, resulting in a suspension solution with a pH below neutral, followed by the addition of a retanning agent, followed by further rotation of the tanning drum for a period of time, followed by draining the suspension solution and rinsing with water. The leather is then dried, such as by hanging it to dry at room temperature without vacuum or in a vacuum chamber. Sulfited polyester is added as a retanning agent in an amount of 2% to 15%, preferably 4% to 12%, and most preferably 6% to 10%, the percentage referring to the weight percentage of the nonvolatile portion of the sulfited polyester compared to the weight of the leather.

[0046] The flexibility of leather can be quantified according to ISO 17235. In this measurement, a steel cylinder of defined mass is pressed into a leather framework at a defined speed and the resulting increased area of ​​the leather is measured. A higher number indicates a larger area, which in turn indicates increased flexibility of the leather.

[0047] The lightfastness of leather can be determined, for example, with a Suntester, in accordance with ISO 105-B02. Retanned leather is typically exposed to light for 24 to 72 hours. The resulting yellowing can be quantified with a spectrophotometer or assigned via the Blue Scale method, assigning a number from 1 to 8 with increasing lightfastness, with a score of 6 or above being considered "good."

[0048] Heat-induced aging of leather can be determined in accordance with ISO 105-A02 by exposing the leather to heat at 100°C for 48 hours and 130°C for 2 hours. After heat exposure, leather samples can be rated according to a gray scale ranging from 1 to 5. Higher numbers indicate greater heat stability, with a score of 3.5 or higher being considered "good."

[0049] Syntans are made from phenol and formaldehyde, and as a result may release formaldehyde, and may contain phenol, bisphenol F, or bisphenol S. Residual monomer analysis for formaldehyde, such as ISO 27587, is widely applied in the leather industry. Bisphenols and phenols can be analyzed in parallel with alkylphenols in ISO 18218-1. Advantageously, retanning agents containing sulfited polyesters are free of formaldehyde, phenol, and bisphenol, where free of formaldehyde, phenol, and bisphenol means that the concentration of formaldehyde, phenol, and bisphenol is less than 10 ppm, preferably less than 2 ppm.

[0050] The solidity of retanned leather is determined mainly via the sense of touch. Solidity is an aesthetic quality parameter and an organoleptic property defined by the spacing between the fibers, which (by the sense of touch) indicates a high or low amount of fibers per area. This is the result of good filling of the interfiber spaces and proper lubrication of the fibers to avoid clumping.

[0051] Grain firmness is a rating of the top layer of leather after bending it with both hands. The smoother the layer, the firmer the bent leather will be. The more wrinkles present, the less firm it will be.

[0052] The solidity and firmness of retanned leather is determined via touch and is generally graded numerically, the lower the number the better.

[0053] The sulfited polyesters can be used to prepare leathers for a variety of uses, such as shoe, furniture, car, clothing, and bag leathers.

[0054] Any type of conventionally treated leather is suitable for treating by using sulfited polyesters, in particular grain leathers (e.g., nappa leather from sheep, goat, or cow, and box leather from calf or cow), suede leathers (e.g., velour leather from sheep, goat, or calf, and hunting leather), split velour (e.g., from cow or calf skins), buckskin and nubuck leathers, as well as wool skins and fur (e.g., suede leather with fur).

[0055] Leather can be of various thicknesses such as 0.5mm to 8mm, thus thin leather is suitable for clothing leather or glove leather (nappa), medium thickness leather is suitable for shoe upper leather and handbags, thick leather is also used for shoe sole leather, furniture leather, suitcases, belts and sporting goods leather, hairy leather and fur can also be used.

[0056] The leather obtained by treatment with the sulfited polyester may then be further processed by any of the processes conventionally used in the leather industry, such as bleaching, coloring, dyeing, fatliquoring, dry setting, conditioning, staking, milling, tumbling, buffing, pressing, embossing, ironing, and coating.

[0057] Sulfited polyesters represent a novel, non-toxic and partially or fully renewable alternative to oil-based phenol-formaldehyde condensates in the leather industry.

[0058] Sulfited polyesters can be used as retanning agents for leather treatments that are superior to syntans in properties such as flexibility, solidity, and light-induced aging, while solving the problem of formaldehyde, phenol, or bisphenol moieties and allowing for partially or fully renewable non-toxic starting materials.

[0059] The present invention is further illustrated by the following non-limiting examples. [Example]

[0060] The starting materials used in these examples were commercially available and were used without further purification. The preferred acid catalyst for esterification is sulfuric acid or paratoluenesulfonic acid, abbreviated as pTSA. Nuclear magnetic resonance was measured on a 400 MHz spectrometer. The solid content of the aqueous solution was determined with a Mettler Tolodo HG53 water analyzer. Bis-(3-hydroxypropyl)succinate (CAS 1646623-97-3) was synthesized according to Papageorgiou, G.; Vassiliou, A.; Karavelidis, V.; Koumbis, A.; Bikiaris, D.; Macromolecules 2008, 41(5), 1675-1684.

[0061] Intermediate 1: Ester of bis-(3-hydroxypropyl)-succinate with maleic anhydride [ka] In a 100 mL single-neck flask equipped with a water separator under a reflux condenser, 46.8 g of bis-(3-hydroxypropyl)-succinate (M = 234 g / mol, 0.2 mol, 1.00 equiv.) was treated with 39.2 g of maleic anhydride (M = 98 g / mol, 0.4 mol, 2.00 equiv.) at 70° C. The reaction mixture was heated to 120-140° C. and stirred for 2 h.

[0062] 1 g of the viscous reaction mixture was dissolved in 10 mL of ethanol and 30 mL of water. The pH was measured to be 2.2. Titration with 0.1 N NaOH: 4.65 mL of 1 N NaOH was needed to neutralize two COOH moieties, and 5 mL of 0.1 N NaOH was consumed to reach pH = 7. 80 g of a very viscous oil was obtained. M = 430 g / mol.

[0063] 1H-NMR(400MHz,CDCl3):1.75-2.02(m,4H,CH2),2.50-2.60(m,4H,CH2-C=O),4,02-4.2 5(m,8H,OCH2),6.25-6.28(m,2H,C=CH),6.90-6.94(m,2H,C=CH),11.2(sbr,2H,COOH).

[0064] 1,3-propanediol and succinic acid can be readily sourced biobased, and maleic acid is petrochemically derived, allowing 10 of the 18 carbons in Intermediate 1 to be biobased.

[0065] Example 1: Sulfitation of Intermediate 1 with NaSO [ka] In a 250 mL single-neck flask equipped with a reflux condenser, 27.5 g of intermediate 1 (M = 430 g / mol, 63.9 mmol) was suspended in 60 mL of warm water to produce a two-phase suspension. 12.2 g of NaSO (M = 190 g / mol, 0.035 mol) was added. The two-phase suspension was treated with 9.8 g of 25% aqueous ammonia (144 mmol) to raise the pH to 8. The suspension was heated to 80 °C for 2 hours: Phase 1: pH = 7.5. The pale yellow solution was acidified with 4 mL of 85% aqueous formic acid to produce a pH of 4.5. A yellow solution with a solids content of 38% was obtained in an amount of 95 g.

[0066] 1H-NMR(400MHz,D2O):1.84-1.92(m,4H,CH2),2.36-2.94(m,10H,CH2-C=O;CH-SO3Na),4.04-4.14(m,8H,OCH2).

[0067] No additional carbon is introduced during sulfitation, therefore the carbon ratio of Example 1 is the same as Intermediate 1: 10 of the 18 carbons can be biobased.

[0068] Intermediate 2: Polyester of propane-1,3-diol and succinic acid (n=3) [ka] In a 250 mL single-neck flask equipped with a reflux condenser and a water separator, 76 g of propane-1,3-diol (M = 76 g / mol, 1 mol = 1.00 equiv.) was treated with 88.56 g of succinic acid (M = 118 g / mol, 0.75 equiv.) and 0.36 g of pTSA. The mixture was heated to 140-160 °C for 3 h. 24 g of water (M = 18 g / mol, 1.5 mol, required distillation) and 21 g of water were obtained. The theoretical yield was 140.9 g. 140 g of a yellow oil with low viscosity was obtained, M = 550 g / mol (n = 3).

[0069] 1H-NMR(400MHz,CDCl3):1.80-1.88(m,4H,CH2),1.90-1.98(m,4H,CH2),2.56-2.64(m,12H,CH2-C= O),3.00(sbr,2H,OH),3.64-3.72(m,4H,CH2OH),4.10-4.18(m,8H,OCH2),4.22-4.27(m,4H,OCH2).

[0070] 1,3-propanediol and succinic acid can be readily sourced biobased, allowing all carbons (24, n=3) in Intermediate 2 to be biobased.

[0071] Intermediate 3: Polyester of Intermediate 2 (n=3) with 2 equivalents of maleic anhydride [ka] In a 250 mL single-neck flask equipped with a reflux condenser, 30 g of intermediate 2 (M = 550 g / mol, 0.054 mol = 1.00 equiv) was treated with 10.7 g of maleic anhydride (M = 98 g / mol, 0.108 mol, 2.00 equiv) at 70° C. The reaction mixture was heated to 140° C. and stirred for 2 h.

[0072] 0.31 g of the reaction mass was dissolved in 20 mL of a 1 / 1 mixture of ethanol and water. The pH was 2.5. To neutralize two equivalents of COOH groups, 8.3 g of 0.1 N aqueous sodium hydroxide was required, and 8.6 g of 0.1 N aqueous sodium hydroxide was required to reach a pH of 7. A 40 g quantity of viscous oil was obtained. M = 747 g / mol.

[0073] 1H-NMR(400MHz,CDCl3):1.85-1.89(m,4H,CH2),1.90-1.98(m,4H,CH2),2.56-2.58(m,12H,CH2-C=O),4.10-4.1 8(m,12H,CH2O),4.10-4.18(m,4H,OCH2),6.20-6.22(m,2H,C=CH),6.28-6.30(m,2H,C=CH),8.50(sbr,2H,COOH).

[0074] Although maleic acid is petrochemically derived, all carbons in Intermediate 2 can be biobased, which makes 24 of the 32 (n=3) carbons in Intermediate 3 biobased.

[0075] Example 2: Sulfitation of Intermediate 3 (n=3) with NaSO [ka] In a 250 mL single-neck flask equipped with a reflux condenser, 46 g of intermediate 3 (n = 3, M = 747 g / mol, 61.65 mmol) was suspended in 80 mL of warm water and treated with 6 mL of 25% aqueous ammonia to raise the pH to 7. 11.2 g of pure NaSO (M = 190 g / mol, 58.00 mol) was added. The suspension was heated to 80 °C for 2 hours, yielding a one-phase product with a pH of 5.0. A yellow solution with a solids content of 31% was obtained in an amount of 140 g.

[0076] 1H-NMR(400MHz,D2O):1.78-1.96(m,8H,CH2),2.40-2.50(m,2H,CH2-C=O),2.52 -2.60(m,12H,CH2-C=O),2.80-3.15(m,2H,CH-SO3Na),4.00-4.16(m,16H,OCH2).

[0077] No additional carbon is introduced during sulfitation, therefore the carbon ratio of Example 2 is the same as Intermediate 3: 24 of the 32 (n=3) carbons can be biobased.

[0078] Intermediate 4: Polyester of propane-1,3-diol and succinic acid (n=4) [ka] In a 500 mL single-neck flask equipped with a water separator under a reflux condenser, 152.2 g of propane-1,3-diol (M = 76 g / mol, 2 mol = 1.00 equiv.) was treated with 188.9 g of succinic acid (M = 118 g / mol, 1.6 mol, 0.8 equiv.) and 0.36 g of pTSA. The mixture was heated to 140-160 °C for 3 h. 57.6 g of water (M = 18 g / mol, 3.2 mol, required removal by distillation) and 50 g of water were obtained. The theoretical yield was 283.90 g, and 280 g of a yellow oil was obtained. M = 709 g / mol, (C 31 H 48 O 18 ).

[0079] 1H-NMR(400MHz,CDCl3):1.78-1.84(m,4H,CH2),1.92-1.98(m,6H,CH2),2.52-2.58(m,16H,CH2-C= O),3.25(sbr,2H,OH),3.62-3.66(m,4H,CH2OH),4.10-4.14(m,12H,OCH2),4.16-4.20(m,4H,OCH2).

[0080] 1,3-propanediol and succinic acid can be readily sourced biobased, allowing all carbons (31, n=4) in Intermediate 2 to be biobased.

[0081] Intermediate 5: Polyester of Intermediate 4 (n=4) with 2 equivalents of maleic anhydride [ka] In a 250 mL single-neck flask equipped with a water separator under a reflux condenser, 140 g of intermediate 4 (M = 709 g / mol, 197.5 mmol = 1 equiv.) was treated with 38.7 g of maleic anhydride (M = 98 g / mol, 0.395 mol, 2.00 equiv.) at 70 °C. The reaction mixture was heated to 120 °C-140 °C and stirred for 2 h.

[0082] 1.07 g of the reaction mass was dissolved in 10 mL of ethanol and 20 mL of water was added, resulting in a white suspension with a pH of 2.0. Titration with 0.1 N aqueous sodium hydroxide required 30 mL and consumed 27.2 mL. A very viscous oil was obtained in an amount of 164 g (theoretical yield of 178 g). M = 905 g / mol.

[0083] 1H-NMR(400MHz,CDCl3):1.86-1.92(m,6H,CH2),1.94-1.98(m,4H,CH2),2.52-2.58(m,16H,CH2-C=O), 4.08-4.16(m,12H,CH2OH),4.22-4.28(m,4H,OCH2),6.20(d,J=2Hz,4H,HC=CH),10.42(sbr,2H,COOH).

[0084] Although maleic acid is petrochemically derived, all carbons in Intermediate 4 can be biobased, making 31 of the 39 (n=4) carbons in Intermediate 3 biobased.

[0085] Example 3: Sulfitation of Intermediate 5 (n=4) with NaSO [ka] In a 250 mL single-neck flask equipped with a reflux condenser, 25 g of intermediate 5 (n = 4, M = 905 g / mol, 27.6 mmol) was suspended in 60 mL of warm water. A 5.3 g quantity of NaSO (M = 190 g / mol, 27.6 mmol) was added. The suspension was treated with 13.8 g of 25% aqueous ammonia (200 mmol) to raise the pH to 7, and the mixture was subsequently heated to 90 °C for 2 hours, resulting in a one-phase product with a pH of 5.6. A 101 g quantity of yellow solution with a solids content of 36.6% was obtained.

[0086] 1H NMR in DO: Compared to intermediate 5, no olefinic signals were identified and new CH and CH2 signals were formed. Complex NMR signals due to positional isomers.

[0087] No additional carbon is introduced during sulfitation, therefore the carbon ratio of Example 3 is the same as Intermediate 5: 31 of the 39 (n=4) carbons can be biobased.

[0088] Intermediate 6: Polyester of bis-(3-hydroxypropyl)-succinate with 0.5 equivalents of itaconic acid [ka] In a 100 mL single-neck flask equipped with a water separator under a reflux condenser, 46.8 g of bis-(3-hydroxypropyl)-succinate (M = 234 g / mol, 200 mmol = 1 equivalent) was treated with 13 g of itaconic acid (M = 130 g / mol, 100 mmol, 0.5 equivalent). A 0.3 g amount of pTSA and a 0.6 g amount of 4-methoxyphenol were added. The reaction mixture was heated to 160 °C for 1 hour. 1.8 g of water (which had to be removed by distillation) and 1.7 g of water were obtained.

[0089] The theoretical yield was 59.5 g, and 57.9 g of a medium viscosity oil was obtained. M = 563 g / mol.

[0090] 1H-NMR(400MHz,CDCl3):1.74-1.85(m,4H,CH2),1.88-1.98(m,4H,CH2),2.56-2.64(m,8H,CH2-C=O),3.28-3.32(s,2H CH2-C=O),3.62-3.68(m,4H,CH2-OH),4.08-4.12(m,8H,OCH2),4.14-4.18(m,4 H,OCH2),4.40(sbr,2H,OH),5.64-5.72(m,1H,C=CH),6.24-6.34(m,1H,C=CH).

[0091] 1,3-propanediol, succinic acid, and itaconic acid can be readily sourced biobased, allowing all the carbon in intermediate 6 to be biobased.

[0092] Example 4: Sulfitation of Intermediate 6 with NaSO [ka] In a 100 mL single-neck flask equipped with a reflux condenser, 25 g of intermediate 6 (M = 563 g / mol, 44 mmol) was suspended in 60 mL of warm water. A 5.3 g quantity of NaSO (M = 190 g / mol, 22 mmol) was added. The suspension was treated with 9.8 g of 25% aqueous ammonia (144 mmol) to raise the pH to 9, and the mixture was subsequently heated to 90 °C for 2 hours, resulting in a one-phase product with a pH of 8.5. A colorless solution with a solids content of 33% was obtained in an amount of 91.6 g.

[0093] 1H-NMR(400MHz,D2O):1.72-1.94(m,8H,CH2),2.60-2.66(m,8H,CH2-C=O),2.78-3.42 (m,5H,CH-CH2-C=O,CH2-SO3Na),3.68-3.76(m,4H,CH2OH),4.02-4.16(m,12H,OCH2).

[0094] No additional carbon is introduced during sulfitation, therefore the carbon ratio of Example 4 is the same as Intermediate 6: all carbon can be biobased.

[0095] Intermediate 7: Polyester of bis-(3-hydroxypropyl)-succinate with 1.5 equivalents of itaconic acid [ka] In a 100 mL single-neck flask equipped with a water separator under a reflux condenser, 23.4 g of bis-(3-hydroxypropyl)succinate (M = 234 g / mol, 100 mmol = 1 equivalent) was treated with 19.5 g of itaconic acid (M = 130 g / mol, 150 mmol, 1.5 equivalents). 0.15 g of pTSA and 0.42 g of 4-methoxyphenol were added. The reaction mixture was heated to 160 °C for 1 hour. 3.6 g of water (which had to be removed by distillation) and 3.2 g of water were obtained. The theoretical yield was 42 g, and 40.1 g of a medium-viscosity oil was obtained. M = 787 g / mol.

[0096] 1H-NMR(400MHz,CDCl3):1.75-1.98(m,8H,CH2),2.50-2.68(m,8H,CH2-C=O),3.20-3.28(m,6H,CH2-C =O),4.02-4.22(m,16H,OCH2),5.60-5.75(m,1H,C=CH),6.22-6.34(m,1H,C=CH),8.60(sbr,2H,COOH).

[0097] 1,3-propanediol, succinic acid, and itaconic acid can be readily sourced biobased, allowing all carbon in intermediate 7 to be biobased.

[0098] Example 5: Sulfitation of Intermediate 7 with NaSO [ka] In a 100 mL single-neck flask equipped with a reflux condenser, 25 g of intermediate 7 (M = 787 g / mol, 24.8 mmol) was suspended in 60 mL of warm water. A 7.1 g quantity of NaSO (M = 190 g / mol, 37 mmol) was added. The suspension was treated with 6.6 g of 25% aqueous ammonia (100 mmol) to raise the pH to 8, and the mixture was subsequently heated to 90 °C for 2 h, resulting in a one-phase product with a pH of 5.6.

[0099] The solution was acidified with 6 mL of 10% aqueous sulfuric acid to reach a pH of 4. A colorless solution with a solid content of 29% was obtained in an amount of 109 g.

[0100] 1H NMR in DO: Compared to intermediate 7, no olefinic signals were identified and new CH and CH2 signals were formed. Complex NMR signals due to positional isomers.

[0101] No additional carbon is introduced during sulfitation, therefore the carbon ratio of Example 5 is the same as Intermediate 7: all carbon can be biobased.

[0102] Example 6: Retanning Treatment Results The new condensates were tested as retanning agents on fur tanned with chromium sulfate. The retanning agent serves to fill the collagen structure and impart properties such as flexibility, grain firmness, and fastness properties. The resulting leather was analyzed and compared with leather retanned with syntan.

[0103] Retanning was performed on wet blue, a leather-making intermediate resulting from the treatment of pelts pickled with 7% chromium sulfate. In a 3.5 L tanning drum, 100 g of water and 100 g of bovine wet blue from southern Germany with a strength of 1.7 mm were treated with 1.2 g of sodium formate and 0.3 g of sodium bicarbonate for 90 minutes. The resulting suspension had a pH of 4.5. 8 g of retanning agent (solids) was added, and rotation of the tanning drum continued for 90 minutes. The suspension was drained, and the leather was washed with 200 g of water. The leather was then dried overnight by hanging without vacuum at room temperature.

[0104] Leather flexibility was quantified according to ISO 17235, where a steel cylinder of defined size is pressed into a leather sample at a defined speed and force, resulting in an area increase of the leather sample, with a higher number representing a larger area, which indicates increased leather flexibility.

[0105] The solidity of the retanned leather was determined via touch, with a lower number indicating better solidity.

[0106] Grain Firmness is a rating of the top layer of leather after bending it with both hands. The smoother the layer, the firmer the bent leather will be; the more wrinkles present, the less firm it will be. A lower number indicates better firmness.

[0107] To determine lightfastness, leather was exposed to light for 72 hours in a Suntester in accordance with ISO 105-B02 (also known as Xenotest). After exposure to light, leather samples were rated according to a blue scale ranging from 1 to 8. Higher numbers indicate less color change and therefore greater resistance to light-induced aging.

[0108] To determine heat-induced ageing, leather was exposed to heat at 100°C for 48 hours and 130°C for 2 hours according to ISO 105-A02. After heat exposure, the leather samples were rated according to a grey scale ranging from 1 to 5, with higher numbers indicating greater thermal stability.

[0109] Leather was retanned according to examples 1, 2, 3, 4 and 5 and compared with leather retanned with commercial phenolic syntan and with a blank, representing a strip of wet blue treated with water instead of polycondensate. The results are collected in Table 1. [Table 1]

[0110] As can be seen from Table 1, all leathers retanned with sulfited polyesters from Examples 1 to 5 showed better softness results in the IUP measurements than leathers treated with syntan, with higher numbers representing larger areas, which indicates increased softness of the leather.

[0111] The leathers retanned with sulfited polyesters from Examples 2 and 4 achieved better solidity than the leathers treated with syntan. Lower values ​​indicate better solidity. Blank leather achieved the lowest performance in solidity.

[0112] The sulfited polyester retanned leathers from all examples achieved better results in firmness than the leathers treated with syntan, with example 4 being the best and clearly superior to syntan. Lower values ​​indicate better firmness. [Table 2]

[0113] As can be seen from Table 2, the retanned leathers of Examples 2 and 4 performed significantly better in the light-induced aging test than the leathers treated with syntan, and also better than the blanks made without retanning.

[0114] The retanned leathers of Examples 2 and 4 performed significantly better in the heat-induced aging test than the leather treated with syntan, and in the same range as the untreated leather pieces.

[0115] The free formaldehyde content of the sulfited polyester was measured in accordance with ISO 27587 and found to be less than 10 ppm. The bisphenol and phenol content of the syntan was measured in accordance with ISO 18218-1 and found to be 120 ppm for bisphenol S and below the detection limit for phenol and bisphenol F.

[0116] The sulfited polyesters of Examples 1-5 are unable to release formaldehyde due to their different chemical compositions and do not contain phenol or bisphenol. The sulfited polyesters of Examples 4 and 5 contain 4-methoxyphenol as a scavenger, but 4-methoxyphenol is significantly less toxic than phenol.

Claims

1. 1. A process for the production of sulfited polyesters, in which more than 50% of the carbon atoms are derived from bio-based sources, by esterification of an unsaturated carboxylic acid or anhydride thereof, and optionally a saturated carboxylic acid or anhydride thereof, with a polyol at a temperature of 120°C to 180°C, and subsequent sulfitation at a pH value of 7 to 9 and a temperature of 50°C to 120°C, wherein at least one or more of the unsaturated carboxylic acid or anhydride thereof and optionally a saturated carboxylic acid or anhydride thereof is bio-based.

2. 2. The process according to claim 1, wherein said esterification of unsaturated carboxylic acid or its anhydride and optionally saturated carboxylic acid or its anhydride with polyol is carried out at a temperature between 140°C and 160°C, preferably for a reaction duration between 1 and 3 hours.

3. 3. The process according to claim 1 or 2, wherein the sulfitation reaction is carried out at a pH value, at 60°C to 100°C, preferably 70°C to 90°C, for a reaction duration preferably of 1 to 5 hours.

4. 4. The process of any one of claims 1 to 3, wherein the molar ratio of saturated acid to unsaturated acid ranges from 0:1 to 5:

1.

5. 5. The process according to any one of claims 1 to 4, wherein the carboxylic acid (unsaturated and / or saturated) is a dicarboxylic acid, optionally also a monocarboxylic acid (in a molar ratio of monocarboxylic acid to dicarboxylic acid of from 0:100 to 25:75), optionally also a tricarboxylic acid or a polycarboxylic acid (in a molar ratio of tricarboxylic acid or polycarboxylic acid to dicarboxylic acid of from 0:100 to 10:90).

6. The process according to any one of claims 1 to 5, wherein the (un)saturated carboxylic acid is selected from the group of bio-based acids.

7. 7. The process of claim 6, wherein the unsaturated carboxylic acid is selected from the group consisting of glutaconic acid, itaconic acid, citraconic acid, and mesaconic acid.

8. 8. The process of any one of claims 1 to 7, wherein the polyol is selected from the group of bio-based polyols comprising 1,2-ethanediol, 1,3-propanediol, glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, galactitol, fucitol, iditol, inositol, volemitol, isomalt, maltitol, lactitol.

9. A sulfited polyester obtainable by the process defined in any one of claims 1 to 8.

10. 10. The sulfited polyester according to claim 9, having a degree of sulfitation of 95% or more.

11. 11. The sulfited polyester of claim 9 or 10, wherein the concentration of free formaldehyde, bisphenols, and phenol is less than 2 ppm.

12. 12. The sulfited polyester of any one of claims 9 to 11, wherein greater than 50% of the carbon atoms are derived from bio-based sources.

13. 13. Use of a sulfited polyester, preferably as defined in any one of claims 9 to 12, as a retanning agent for the treatment of leather, pre-tanned leather, tanned leather, furs, skins, hides, leather intermediate products or unfinished leather.

14. 14. Use as defined in claim 13 in an amount of 2% to 15%, preferably in an amount of 4% to 12%, most preferably in an amount of 6% to 10%, the percentages referring to the weight percentage of the non-volatile portion of the sulfited polyester compared to the weight of the leather.

15. 13. A process for retanning pre-tanned leather, tanned leather, furs, skins, hides, leather intermediate products or unfinished leather using a sulfited polyester, preferably as defined in any one of claims 9 to 12, as a retanning agent.

16. Leather obtainable by the process according to claim 15.

17. 17. Leather according to claim 16, having good solidity, firmness, good flexibility in accordance with ISO 17235, heat resistance in accordance with ISO 105-A02, and good lightfastness in accordance with ISO 105-B02 and / or ISO 105-B02, wherein good flexibility means 3.0, good heat resistance means 3.5 or higher on a grey scale of 1 to 5, and good lightfastness means 6 or higher on a grey scale of 1 to 8.

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